Foams based on styrene polymers have been known for some time and are widely used by way of example for the production of insulation materials. Alongside the major advantages of these materials, for example in relation to insulation properties, low density, water resistance, and expandability, there are disadvantages in respect of chemicals resistance and impact resistance.
Thermoplastic polyurethanes in foamed form are also known. Examples of their features are excellent resilience, transparency, abrasion resistance, and chemicals resistance, but they have disadvantages such as inadequate dimensional stability and unsatisfactory foamability: it is technically very difficult to produce an expandable moldable foam from TPU, because physical blowing agents such as pentane are very rapidly lost into the environment from TPU via diffusion (poor blowing-agent retention capability). Physical blowing agents in straight TPU cannot moreover generate sufficient foaming pressure, and it is therefore not possible to use an EPS prefoamer for expansion of straight TPU comprising blowing agent.
Attempts have also been made to combine the advantageous properties of foams based on polystyrene and foams based on TPU.
The application WO 2007/082838 describes by way of example the production of expandable TPUs via compounding of TPU with a blowing agent in extrusion-based processes.
WO 2010/010010 describes thermoplastic polymer blends based on thermoplastic polyurethane and styrene polymer, foams produced therefrom, and associated production processes.
JP-A 1980-080440 describes a process for the production of expandable-polymer-particle material where from 20 to 80% by weight of TPU-elastomer-particle material and from 80 to 20% by weight of a monomer or methacrylate ester are suspended in an aqueous medium and polymerized.
JP-A 2007-231068 discloses styrene-modified expandable-TPU-particle material comprising 100 parts by weight of TPU and from 20 to 300 parts by weight of a styrene polymer, where styrene polymer particles of size 0.5 μm or less have been dispersed in the TPU.
Although good results are already being achieved with the known materials, there remains nevertheless much room for improvement, for example in relation to blowing-agent-retention capability combined with high resilience of these materials.